An analytical transmission electron microscope equipped for dispersive x-ray elemental analysis is required for federally funded research projects intended as comprehensive characterizations of (1) small-granule endocrine cells of the lungs, (2) structure-function relationships among granulosa cells of the ovary, (3) microvascular changes in the oral mucosa of diabetic man, and (4) the biology of lysosomal production in activated pulmonary alveolar macrophages. All projects depend principally upon transmission electron microscopy as an investigative tool, and common needs specify an instrument with excellent image contrast and low magnification capability; in addition, the two projects on pulmonary cells call for good imaging characteristics with use of thick (0.5-1.5 Mum) sections. Dispersive x-ray analysis is already in use on the project on pulmonary endocrine cells, and specific applications are described for the projects on granulosa cells and alveolar macrophages. Available instruments are unequal to these requirements, and none are equipped for x-ray analysis.